<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style>
			[title] {
			    font-size: 20px;
				color: aqua;
			}
			[href] a{
				font-size: 20px;
			    color: pink; 
			}
			a[title][href]{
				font-size: 40px;
			    color: chartreuse;
			}
		</style>
	</head>
	<body>
		<h1>可以应用样式：</h1>
		<h2 title="Hello world">Hello world</h2>
		<a title="W3School" href="http://w3school.com.cn">W3School</a>
		<hr />
		<h1>无法应用样式：</h1>
		<h2>Hello world</h2>
		<a href="http://w3school.com.cn">W3School</a>
	</body>
</html>